Bulletin 214, Cotton Diseases in Florida


stable manure seems to especially favor the multiplication of the
worms. The presence of nematodes on cotton should indicate a
special handling of the soil to prevent loss of more susceptible
crops, such as many of the garden or truck crops, and to prevent
the worms from multiplying to such an extent as to become a
serious factor in the growing of cotton. Cotton grown after an
especially susceptible crop is much more severely injured than it is
when grown after an immune crop.
 The young worms are capable of surviving several months of
a non-parasitic existence in the soil. When susceptible hosts are
available, however, the worms bore into the roots just back of
the growing tip, and some toxic substance formed by them stim-
ulates the roots to the development of galls. Young galls are
white in color, but later they become darker in color and irregular
in shape on account of attacks by insects and fungi. Where the
field is heavily infested practically all of the roots are covered
with galls which, in the case of cotton, usually do not exceed a
half inch in diameter, though in certain extremely susceptible
crops the galls may become as large as two inches in diameter.
The female lays eggs in the roots which hatch into the larvae.
The larvae migrate through the roots, causing other galls, or they
may escape into the soil to attack other plants. A female may lay
as many as 500 eggs and under favorable conditions a number of
generations may occur during a year. The injury to the plants
results from the disturbance of the normal water-carrying ca-
pacity of the roots, and the degree of injury is proportional to
the number of galls.
 SYMPTOMS
 Nematode injury to the roots may be manifested above ground
by a yellowing and stunting of the plants. The degree of yellow-
ing or stunting is determined by the severity of the attack on the
roots and varies from an unnoticeable condition to the death of the
plant. The final proof of the presence of this disease is the
finding of galls or knots on the roots of suspicious looking plants
that have been pulled up. The root injury of cotton plants by
nematodes is illustrated in Fig. 4.
 CONTROL
 The only means of controlling root-knot feasible of execution
by the cotton farmer is suitable rotation of crops. Soil infested
with nematodes should not be planted to cotton or any other sus-
ceptible crop. There are a number of crops that are not suscep-